Hearing aids are wearable hearing apparatuses used to assist those with impaired hearing. To meet the numerous individual requirements different designs of hearing aid are provided, such as behind-the ear hearing aids and in-the-ear hearing aids. The typical hearing aids mentioned are worn on the outer ear or in the auditory canal. Above and beyond these designs however there are also bone conduction hearing aids, implantable or vibro-tactile hearing aids available on the market. In such hearing aids the damaged hearing is simulated either mechanically or electrically.
Hearing aids principally have as their main components an input converter, an amplifier and an output converter. The input converter is as a rule a sound receiver, e.g. a microphone, and/or an electromagnetic receiver, e.g. an induction coil. The output converter is mostly implemented as an electroacoustic converter, e.g. a miniature loudspeaker or as an electromechanical converter, e.g. bone conduction earpiece. The amplifier is usually integrated into a signal processing unit. This basic structure is shown in FIG. 1, using a behind-the ear hearing aid 1 as an example. One or more microphones 2 for recording the sound from the surroundings are built into a hearing aid housing 7 for wearing behind the ear. A signal processing unit 3 which is also integrated into the hearing aid housing 7 processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4 which outputs an acoustic signal. The sound is transmitted, if necessary via a sound tube, which is fixed with an otoplastic in the auditory canal, to the hearing aid wearer's eardrum. The power is supplied to the hearing aid and especially to the signal processing unit 3 by a battery 5 also integrated into the hearing aid housing 7. A coil 6 arranged in the hearing aid housing 7 can be used to exchange data inductively in a non-contact manner with another hearing aid or with a remote control.
Charging rechargeable cells or batteries of a hearing aid frequently means taking the rechargeable cell or the battery out of the hearing aid, inserting it in a charger and charging it. After charging as a rule very small and difficult-to-handle batteries must be taken out of the charger and put back into the hearing aid. An alternate charging process consists of leaving the rechargeable cell in the hearing aid and charging it there using a wired system. Corresponding metallic contacts are to be provided on the hearing aid for this purpose. The disadvantage of these contacts is that they mostly protrude from the housing and are not flush with the latter. As a result they can easily get dirty.
The practice of transmitting energy wirelessly to a hearing aid is also known. The energy transfer for this can be undertaken by electrical (capacitive), magnetic (inductive) or electromagnetic fields. Such charging demands at least one additional component in the hearing aid, which converts the corresponding field into electrical energy.
Generally an inductive method is used for wireless charging of rechargeable cells. The transmitter operates with a transmit coil and the receiver of the energy likewise uses a coil for receiving the energy. These types of coil are relatively large, which with hearing aids in particular, runs counter to the constantly strived-for goal of miniaturization.
WO 2007/056421 A2 describes this type of apparatus for wireless charging of a hearing aid battery with coils. In addition to transmission of electrical energy, data can also be transmitted wirelessly.
DE 197 45 101 A1 relates to an in-the-ear hearing aid with a hearing aid charging circuit with a coil for wirelessly receiving electrical energy. Data of a voltage measurement can likewise be received via the coil.
In subsequently published patent application DE 10 2007 009 176 B1 a solution is proposed in which the injection of energy into a hearing aid for charging its rechargeable cell is undertaken using components that occupy as little space as possible. The coil of an earpiece is thus used to couple in energy for charging the rechargeable cell inductively. Alternatively acoustic energy can also be coupled in via the earpiece or the microphones and converted there into electrical energy.